Solar savings calculator

How this solar savings calculator estimates your figures

The calculator above is deliberately simple: three inputs, one indicative answer. Here is what sits behind the numbers, so you can judge how close they are likely to be for your home.

What it uses

• Your electricity usage — taken from your average monthly bill and converted to annual kilowatt-hours at a typical unit rate. That sets the recommended system size, capped between 3 kW and 8 kW.
• Roof orientation — a south-facing roof is treated as 100%. East- or west-facing roofs are scaled to roughly 80–85% of that, and north-facing lower still. The calculator uses a cautious due-north figure, so a north-east or north-west roof that catches morning or evening sun will usually do a little better than shown. Panels still generate on every aspect.
• Battery storage — ticking the box roughly doubles the share of your own solar you are assumed to use at home rather than export.

What it assumes

Install costs are shown with 0% VAT, the rate that applies to qualifying home solar and battery installations until 31 March 2027 (due to return to 5% after that). It also uses one fixed import price per unit and one indicative export price for the electricity you send back to the grid. In reality, Smart Export Guarantee rates vary by supplier and change over time — some pay several times more than others — so the export line is the part most worth checking against your own tariff. Our Smart Export Guarantee guide explains how to compare them.

Why it is an estimate — and what firms it up

The calculator cannot see your roof. It does not know its usable area, pitch, chimneys or the tree that shades it after 3pm, and it assumes your usage and tariff stay flat for 25 years. That is why the payback shown is a guide, not a promise. Payback depends heavily on your tariff, how much of your solar you use yourself and how the system is designed. This calculator is deliberately cautious — it assumes a flat 28p/kWh import rate, a modest 10p/kWh export rate and no future price rises — so its payback figures usually come out longer (often 10 years or more) than a tuned installer quote. With a competitive export tariff and higher self-consumption, UK residential systems typically pay back in around 6–9 years; your free survey will show where your home sits. A free solar survey from our MCS-certified team replaces assumptions with measurements — a system design and panel layout for your actual roof (orientation, pitch and shading), a generation forecast, projected savings and payback, and a fixed-price written quote — and that is the figure worth planning around.